It is well known that exposure to sunlight can pose a number of hazards to the skin. These damaging effects may result not only from sunbathing but also from the sunlight exposure associated with daily outdoor activities. The major short term hazard of prolonged exposure to sunlight is erythema, i.e. sunburn, which primarily results from UV radiation having a wavelength of from about 290 nm to about 320 nm. Over the long term, however, malignant changes in the skin surface often occur. Numerous epideminologic studies demonstrate a strong relationship between sunlight exposure and human skin cancer. Another long term hazard of ultraviolet radiation is premature aging of the skin, which is primarily caused by UVA radiation having a wavelength of from about 320 nm to about 400 nm. This condition is characterized by wrinkling and pigment changes of the skin, along with other physical changes such as cracking, telangiectasis, solar dermatoses, ecchymoses, and loss of elasticity. The adverse effects associated with exposure to UV radiation are more fully discussed in DeSimone, "Sunscreen and Suntan Products," Handbook of Nonprescription Drugs, 7th Ed., Chapter 26, pp. 499-511 (American Pharmaceutical Association, Washington, D.C.; 1982); Grove and Forbes, "A Method for Evaluating the Photoprotection Action of Sunscreen Agents Against UV-A Radiation," International Journal of Cosmetic Science, 4, pp. 15-24 (1982); and U.S. Pat. No. 4,387,089, DePolo, issued Jun. 7, 1983.
As a result of the abovementioned hazards associated with sunlight exposure, the general public's interest in the sun protection product market has grown considerably. Today, there are not only sunscreen products for sunbathing but there are also a variety of personal care products which also contain sunscreens, particularly cosmetic type products which are worn daily. "Personal care products" refer to health and cosmetic beauty aid products generally recognized as being formulated for beautifying and grooming the skin and hair. For example, personal care products include sunscreen products (e.g., lotions, skin creams, etc.), cosmetics, toiletries, and over-the-counter pharmaceutical products intended for topical usage.
Not surprisingly, consumers desire that sunscreen products, particularly daily wear products, be effective, aesthetically pleasing to their senses of sight and feel, and economical. Unfortunately, most commercially available sunscreen products are lacking in one or more of these areas.
For example, most commercial sunscreens utilize high levels of sunscreen actives in order to achieve desired levels of UV protection. These high levels of sunscreen actives not only increase the cost of the product but also tend to contribute to poor aesthetics (e.g., poor skin feel, skin whitening, etc.) and skin irritation.
Many conventional sunscreen products are also deficient due to their inability to provide efficacious protection against broad spectrum UV radiation, i.e., protection against both UVB and UVA radiation. Today, most commercially available sunscreen products are efficient at absorbing UV radiation in the 290 nm to 320 nm UVB region such that sunburn of the skin is prevented. They are less efficient when it comes to absorbing light which falls in the 320 nm to 400 nm UVA region, which leaves the skin vulnerable to premature skin aging. This deficiency is due in part to the limited number of UVA absorbing sunscreen actives which are both commercially available and approved for global use.
A wide variety of sunscreen actives have been used in personal care products. It is desirable that the sunscreen active or active system provide broad spectrum UV protection, particularly protection against both UVA radiation and UVB radiation. In addition, the active should be approved for human use, preferably on a global basis. It is further desirable that these sunscreen actives are formulated to provide stable efficacious, and aesthetically appealing sunscreen products.
Dibenzoylmethane compounds are one class of sunscreen compounds which provide broad spectrum UV protection and are approved for global use. Unfortunately, these sunscreens tend to photodegrade upon exposure to UV radiation thereby reducing their UVA efficacy. One approach to stabilize these types of sunscreens is described in U.S. Ser. No. 07/929,612, Deckner, filed Aug. 13, 1992, involving the use of benzylidene camphor sunscreens to stabilize the dibenzoylmethane compound. Such compositions, however, are not currently approved for global use.
Another class of sunscreen actives known as physical sunblocks have also been used to provide protection to the skin against broad spectrum UV radiation. Physical sunblocks are inorganic compounds which are believed to exert their effects by scattering, reflecting or absorbing UV radiation. See, Sayre, R. M. et al., "Physical Sunscreens," J. Soc. Cosmet. Chem., vol. 41, no. 2, pp. 103-109 (1990). Unfortunately, when used at higher levels, they tend to leave an undesirable white film on the consumer's skin and/or agglomerate in the finished product.
A need therefore remains for stable (including photostable), efficient sunscreen products which provide broad spectrum UV protection (i.e., against both UVA and UVB radiation) in a safe, economical, and aesthetically appealing manner (on-skin transparency and low skin irritation).
It has now been found that the compositions hereof having a Sunscreen Efficiency Index of at least about 1.75, a UVA Efficacy Value of at least about 0.5, a UVA Photostability Index of at least about 0.85, a UVB Photostability Index of at least about 0.85, and a Transparency Value of less than about 10 have excellent stability, efficiency, UV protection efficacy, safety, economy and aesthetics.